The present invention relates to a synthetic resin container closure formed from a synthetic resin material as a single unit and, more specifically, to a synthetic resin container closure which has a circular top panel wall and a cylindrical skirt wall extending downwardly from the peripheral edge of this top panel wall, one or two cylindrical sealing protrusions that extend downwardly being formed on the inner surface of the top panel wall.
A synthetic resin container closure which is wholly formed from an appropriate synthetic resin such as polypropylene or polyethylene as a single unit has been proposed as a container closure for drink or beverage containers and has been put to practical use. The container closure has a circular top panel wall and a cylindrical skirt wall extending downwardly from the peripheral edge of this top panel wall, and one or two cylindrical sealing protrusions extending downwardly are formed on the inner surface of the top panel wall. In a container closure disclosed in FIG. 3 of Japanese Unexamined Laid-Open Patent Publication 10-35699, two cylindrical protrusions, that is, an outer cylindrical protrusion and an inner cylindrical sealing protrusion both extending downwardly, are formed on the inner surface of the top panel wall. On the inner surface of the top panel wall is further formed an annular sealing ridge adjacent to the base portion of the outer cylindrical protrusion. The trade name of a product, the name of a manufacturer or distributor and the like are printed on the outer surface of the top panel wall by offset printing, for example. A female thread is formed on the inner peripheral surface of the skirt wall. This container closure is mounted on a container having a male thread formed on the outer peripheral surface of a mouth-neck portion. When the female thread of the container closure is screwed onto the male thread of the mouth-neck portion to mount the container closure on the mouth-neck portion, the inner cylindrical sealing protrusion is brought into close contact with the inner peripheral surface of the mouth-neck portion, and the annular sealing ridge is also brought into close contact with the boundary region between the outer peripheral surface and the top surface of the mouth-neck portion. The outer cylindrical protrusion is brought into not close contact, but relatively loose contact with the outer peripheral surface of the mouth-neck portion to assist close contact of the annular sealing ridge with the boundary region between the outer peripheral surface and the top surface of the mouth-neck portion.
However, the above container closure of the prior art involves the following problems to be solved. Firstly, in the above container closure of the prior art, it is necessary to fully and surely satisfy the basic requirement that when the container closure is mounted on the mouth-neck portion of the container, the mouth-neck portion is sealed hermetically without fail and when the mouth-neck portion is to be opened, appropriate torque is applied to the container closure to turn the container closure, without requiring excessive torque, so that the container closure can be removed from the mouth-neck portion. In addition, it is important that when the mouth-neck portion is to be opened, the sealing of the mouth-neck portion should be released after the container closure is turned at an angle larger than the required rotation angle. Describing this point in more detail, a weakening line is generally formed in the skirt wall of the container closure such that it extends in a circumferential direction, the skirt wall is divided into a main portion above the weakening line and a tamper-evident skirt portion below the weakening line, the above female thread is formed on the inner peripheral surface of the main portion, and an engaging means having an appropriate shape is formed on the inner peripheral surface of the tamper-evident skirt portion. When the container closure is mounted on the mouth-neck portion of the container, the engaging means is engaged with an engaging jaw portion formed on the outer peripheral surface of the mouth-neck portion. When the container closure is turned in an opening direction to open the mouth-neck portion of the container, the weakening line is at least partially broken, whereby the engagement of the engaging means with the engaging jaw portion is released, and the container closure is allowed to be removed from the mouth-neck portion. It is important that when the container closure is turned in the opening direction, the sealing of the mouth-neck portion should be released after the weakening line is at least partially broken. If the sealing of the mouth-neck portion is released before the weakening line is at least partially broken, there occurs such a situation that though the container closure has been tampered to be turned in the opening direction and the sealing of the mouth-neck portion has been released, the weakening line is not broken, and accordingly an indication that the container closure has been tampered and the sealing of the mouth-neck portion has been released does not remain. Therefore, in the above container closure of the prior art, there is a tendency that the sealing of the mouth-neck portion is released before the container closure is turned at a predetermined rotation angle owing to the production tolerance of the container closure and/or the mouth-neck portion or owing to the thermal deformation of the container closure and/or the mouth-neck portion, and there may occur a case where the above basic requirement can not be satisfied.
Secondly, the above container closure is formed from an appropriate synthetic resin by compression molding or injection molding. The molding efficiency of the molding step greatly depends on the required cooling time in the mold, as is well known to people having ordinary skill in the art. When the molded container closure is removed from the mold before the passage of the required cooling time, deformation greater than the permissible range may occur in the circular top panel wall. More specifically, there is a tendency for the center of the top panel wall to be indented, and consequently the top panel wall has a depressed shape more than the permissible range. To shorten the required cooling time without causing deformation greater than the permissible range in the top panel wall, it is known for the thickness of the top panel wall, particularly the center portion positioned on the inner side of the inner cylindrical sealing protrusion, to be reduced to promote the cooling of the top panel wall, particularly the center portion thereof. However, when the thickness of the top panel wall, particularly the center portion thereof, is reduced, another problem arises as follows. When the outer surface of the top panel wall is to be printed, the container closure is mounted on a mandrel to contact the top surface of the mandrel to the inner surface of the center portion of the top panel wall, and then an offset printing roller made from a material having elasticity, such as synthetic rubber, is applied to the outer surface of the top panel wall of the container closure in a printing area. Even when the outer surface of the top panel wall has some distortion of ordinary permissible degree, it is important for carrying out fully satisfactory printing that the printing roller should be compressed by approximately 1 mm when the printing roller is applied to the outer surface of the top panel wall of the container closure. In this case, when the thickness of the top panel wall is reduced to 1 mm for example, the space between the peripheral surface of the printing roller and the top surface of the mandrel to which the container closure is not mounted must be set to substantially zero. In a case of the setting being made like this, if the mandrel is moved through the printing area without the container closure mounted thereon for some accidental reason, printing ink will be adhered to the top surface of the mandrel, and the inner surface of the center portion of the top panel wall of the container closure will be stained by the printing ink when the container closure is then mounted on this mandrel. When the space between the top surface of the mandrel and the peripheral surface of the printing roller is made large to prevent this situation, the amount of compression of the printing roller at the time when the printing roller is applied to the outer surface of the top panel wall of the container closure mounted on the mandrel becomes too small, thereby making it impossible to carry out satisfactory printing in a case where the outer surface of the top panel wall has some general permissible distortion. Further, if the thickness of the top panel wall, particularly the center portion, is reduced, the rigidity of the top panel wall is inevitably reduced, whereby the so-called flexibility of the inner cylindrical sealing protrusion becomes too large, contact pressure between the inner cylindrical sealing protrusion and the inner peripheral surface of the mouth-neck portion of the container becomes too small, and hence the hermetical sealing of the mouth-neck portion is liable to be insufficient.
It is therefore the first object of the present invention to provide a novel and improved synthetic resin container closure which can seal hermetically the mouth-neck portion of a container fully reliably when it is mounted on the mouth-neck portion of the container, can be removed from the mouth-neck portion by applying appropriate torque to turn it without requiring excessive torque, so as to open the mouth-neck portion, and simultaneously can release the hermetical sealing of the mouth-neck portion after turning it at an angle larger than the required rotation angle to open the mouth-neck portion.
It is the second object of the present invention to provide a novel and improved synthetic resin container closure which does not cause any inconvenience in the printing step and does not cause unsatisfactory sealing of the mouth-neck portion of a container even though the cooling time required for compression molding or injection molding can be considerably reduced.
According to the first aspect of the present invention, there is provided a container closure which has a circular top panel wall and a cylindrical skirt wall extending downwardly from the peripheral edge of the top panel wall and which is formed from a synthetic resin as a single unit, wherein
an outer cylindrical sealing protrusion extending downwardly, an inner cylindrical sealing protrusion extending downwardly and an annular sealing ridge located between the outer cylindrical sealing protrusion and the inner cylindrical sealing protrusion and projecting downwardly are formed on the inner surface of the top panel wall;
when the container closure is mounted on the mouth-neck portion of a container, the inner peripheral surface of the outer cylindrical sealing protrusion is brought into close contact with the outer peripheral surface of the mouth-neck portion, the outer peripheral surface of the inner cylindrical sealing protrusion is brought into close contact with the inner peripheral surface of the mouth-neck portion, and the annular sealing ridge is brought into close contact with the top surface of the mouth-neck portion; and
in a state before the container closure is mounted on the mouth-neck portion of the container, the minimum internal diameter D1 of a portion, that is to be brought into close contact with the outer peripheral surface of the mouth-neck portion, of the inner peripheral surface of the outer cylindrical sealing protrusion is smaller than the external diameter D2 of the outer peripheral surface, that is to be brought into close contact, of the mouth-neck portion and satisfies 0.05 mmxe2x89xa6(D2xe2x88x92D1)xe2x89xa60.60 mm, and the maximum external diameter D3 of a portion, that is to be brought into close contact with the mouth-neck portion, of the outer peripheral surface of the inner cylindrical sealing protrusion is larger than the internal diameter D4 of the inner peripheral surface, that is to be brought into close contact, of the mouth-neck portion and satisfies 0.25 mmxe2x89xa6(D3xe2x88x92D4)xe2x89xa61.50 mm.
The container closure provided according to the first aspect of the present invention can be advantageously used when a container formed from an appropriate synthetic resin such as polyethylene terephthalate (the present invention is not limited to this) is filled with contents heated at approximately 80 to 95xc2x0 C. (so-called hot packing). As is well known to people having ordinary skill in the art, after the synthetic resin container to be filled with contents heated at approximately 80 to 95xc2x0 C. is molded into a predetermined shape, the mouth-neck portion thereof is crystallized by heating, thereby slightly reducing the dimensional accuracy of the mouth-neck portion.
Preferably, the outer peripheral surface of the inner cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex81 with respect to the center axis of the container closure and then, extends downwardly in such a manner that it is inclined inward in a radial direction at an inclination angle xcex82 with respect to the center axis. The inclination angle xcex81 may be 5 to 25xc2x0 and the inclination angle xcex82 may be 5 to 30xc2x0. The inner peripheral surface of the inner cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex83 with respect to the center axis, and then, extends substantially parallel with the center axis. Preferably, the outer peripheral surface of the inner cylindrical sealing protrusion has the maximum external diameter D3 at a position below, and away from, the inner surface of the top panel wall by a length L1 of 2.50 to 3.50 mm. In a preferred embodiment, the inclination angle xcex83 of the inner peripheral surface of the inner cylindrical sealing protrusion is larger than the inclination angle xcex81 of the outer peripheral surface of the inner cylindrical sealing protrusion at a position above the portion having the maximum external diameter D3. The inner peripheral surface of the outer cylindrical sealing protrusion extends downwardly in such a manner that it is inclined inward in a radial direction at an inclination angle xcex84 with respect to the center axis, and then, extends downward in such a manner that it is inclined outward in a radial direction. The inclination angle xcex84 may be 13 to 23xc2x0. The outer peripheral surface of the outer cylindrical sealing protrusion extends downwardly in such a manner that it is inclined inward in a radial direction at an inclination angle xcex85 with respect to the center axis. The inclination angle xcex85 is larger than the inclination angle xcex84 and may be 15 to 25xc2x0. Preferably, the inner peripheral surface of the outer cylindrical sealing protrusion has the minimum internal diameter D1 at a position below, and away from, the inner surface of the top panel wall by a length L2 of 0.60 to 1.50 mm.
If (D2xe2x88x92D1) and (D3xe2x88x92D4) are too small, a tendency occurs that the hermetical sealing of the mouth-neck portion may become unsatisfactory, and at the same time the sealing of the mouth-neck portion may be released before the container closure is turned at a required rotation angle to open the mouth-neck portion. On the other hand, if (D2xe2x88x92D1) and (D3xe2x88x92D4) are too large, there is a tendency that torque to be applied to the container closure to open the mouth-neck portion may become excessive.
According to a second aspect of the present invention, to attain the second object of the present invention, there is provided a container closure which has a circular top panel wall and a cylindrical skirt wall extending downwardly from the peripheral edge of the top panel wall, a cylindrical sealing protrusion extending downwardly to be brought into close contact with the inner peripheral surface of the mouth-neck portion of a container being formed on the inner surface of the top panel wall, and which is formed from a synthetic resin as a single unit, wherein
a plurality of ribs are formed on the inner surface of a center portion located on the inner side of the cylindrical sealing protrusion of the top panel wall, the thickness T1 of the center portion of the top panel wall is 0.80 to 1.20 mm, the thickness T2 of each of the ribs is 0.20 to 1.00 mm, and the total (T1+T2) of the thickness T1 and the thickness T2 is 1.20 to 1.80 mm.
Preferably, the thickness T1 is 0.90 to 1.10 mm, the thickness T2 is 0.30 to 0.50, and the total (T1+T2) of the thickness T1 and the thickness T2 is 1.30 to 1.50 mm. In a preferred embodiment, the ribs extend radially. The ribs are arranged at equiangular intervals and extend continuously from the center of the center portion to the peripheral edge of the top panel wall. The ribs have a rectangular cross sectional form, and when in a bottom view the area of the center portion of the top panel wall is represented by S1 and the total area of the ribs is represented by S2, S1 and S2 satisfy 0.10S1 less than S2 less than 0.40S1, preferably 0.15S1 less than S2 less than 0.35S1.
If the thickness T1 of the center portion of the top panel wall is too large, the thickness T2 of each of the ribs is too large, or the total of the thickness T1 of the center portion of the top panel wall and the thickness T2 of each of the ribs is too large, the cooling time required for preventing deformation larger than the permissible range in the top panel wall will become long. If the thickness T1 of the center portion of the top panel wall is too small, the rigidity of the top panel wall will become too low and the hermetical sealing of the mouth-neck portion of the container will become insufficient. If the thickness T2 of each of the ribs is too small or the total of the thickness T1 of the center portion of the top panel wall and the thickness T2 of each of the ribs is too small, the rigidity of the top panel wall will become too low and at the same time, it becomes necessary to set the space between the top surface of a mandrel and the peripheral surface of a printing roller to an extremely small value in the printing step, and there is a possibility that the inner surface of the center portion of the top panel wall is stained by a printing ink as described above.
Further, according to a third aspect of the present invention, to attain the first object of the present invention, there is provided a container closure which has a circular top panel wall and a cylindrical skirt wall extending downwardly from the peripheral edge of the top panel wall and which is formed from a synthetic resin as a single unit, wherein
an outer cylindrical sealing protrusion extending downwardly, an inner cylindrical sealing protrusion extending downwardly and an annular sealing ridge which is located between the outer cylindrical sealing protrusion and the inner cylindrical sealing protrusion and projects downwardly are formed on the inner surface of the top panel wall;
when the container closure is mounted on the mouth-neck portion of a container, the inner peripheral surface of the outer cylindrical sealing protrusion is brought into close contact with the outer peripheral surface of the mouth-neck portion, the outer peripheral surface of the inner cylindrical sealing protrusion is brought into close contact with the inner peripheral surface of the mouth-neck portion, and the annular sealing ridge is brought into close contact with the top surface of the mouth-neck portion;
in a state before the container closure is mounted on the mouth-neck portion of the container, the maximum external diameter D3 of a portion to be brought into close contact with the inner peripheral surface of the mouth-neck portion, of the outer peripheral surface of the inner cylindrical sealing protrusion is larger than the internal diameter D4 of the inner peripheral surface to be brought into close contact, of the mouth-neck portion and satisfies 0.25 mmxe2x89xa6(D3xe2x88x92D4)xe2x89xa61.50 mm; and
the inner peripheral surface of the outer cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex86 with respect to the center axis, and then, extends downwardly and radially outwardly in an arc form.
The container closure provided according to the third aspect of the present invention can be advantageously used when a container formed from an appropriate synthetic resin such as polyethylene terephthalate is filled with contents having a normal temperature in a germ-free or germ reduced state (so-called aseptic filling). As is well known to people having ordinary skill in the art, the synthetic resin container filled with contents having a normal temperature has a mouth-neck portion with fairly high dimensional accuracy because the mouth-neck portion is not crystallized by heating.
Preferably, the outer peripheral surface of the outer cylindrical sealing protrusion extends substantially parallel with the center axis. Preferably, the outer peripheral surface of the inner cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex81 with respect to the center axis of the container closure and then, extends downwardly in such a manner that it is inclined inward in a radial direction at an inclination angle xcex82 with respect to the center axis. The inclination angle xcex81 may be 5 to 25xc2x0. Preferably, the inner peripheral surface of the inner cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex83 with respect to the center axis and then, extends substantially parallel with the center axis. Preferably, the outer peripheral surface of the inner cylindrical sealing protrusion has the maximum external diameter D3 at a position below, and away from, the inner surface of the top panel wall by a length L1 of 2.50 to 3.50 mm. In a preferred embodiment, the inclination angle xcex83 of the inner peripheral surface of the inner cylindrical sealing protrusion is larger than the inclination angle xcex81 of the outer peripheral surface of the inner cylindrical sealing protrusion at a position above the portion having the maximum external diameter D3.
If (D3xe2x88x92D4) is too small, a tendency occurs that the hermetical sealing of the mouth-neck portion may become unsatisfactory and at the same time, the hermetical sealing of the mouth-neck portion may be released before the container closure is turned at a required rotation angle to open the mouth-neck portion. On the other hand, if (D3xe2x88x92D4) is too large, there is a tendency that torque to be applied to the container closure to open the mouth-neck portion may become excessive. The inner peripheral surface of the outer cylindrical sealing protrusion extends downwardly in such a manner that it is inclined outward in a radial direction at an inclination angle xcex86 with respect to the center axis and then, extends downwardly and radially outwardly in an arc form, whereby the container closure can be mounted on the mouth-neck portion sufficiently and easily and there is virtually no possibility that the container closure is mounted improperly.